Fish passes

ABSTRACT

A fish pass comprises material ( 1 ) that augments a significant part of the crest of a water penning control structure ( 11 ) and a channel component ( 3 ) to convey water downstream of the water penning control structure ( 11 ), the channel component ( 3 ) having a hinged attachment to the crest of the water penning control structure ( 11 ).

FIELD OF THE INVENTION

This invention relates to fish passes, i.e. devices that allow upstreammigration of fish over water level regulation devices such as tiltingweirs, twin leaf gates and other water penning structures. The inventionhas been developed in relation to eel passes, but has application tofish passes generally.

As part of their life cycle, eels migrate upstream in rivers, which arehighly regulated resources with many control structures on them. Thesecontrol structures pen back water at certain times of the year and allowflood water to dissipate at other times. Historically, these structureswere of timber and/or were of such an age that their wetted surfaceswere covered with moss and other natural materials in which the eelscould get purchase and ascend such surfaces.

There has, however, been a recent move to replace traditional penningdevices with modern stainless steel and plastic structures. Examples ofthese are the tilting weir and the twin leaf gate. These latter kinds ofstructures prevent upstream migration of eels by virtue of their sheer,smooth sides and confusing overflow characteristics—eels navigate overmore natural barriers by moving upstream against an attracting flowthrough a suitable substrate.

Large scale eel passes use a pumped water flow as an attractant, butthey are only viable on very large in-river barriers, are expensive torun and the pumps frequently clog.

It is accordingly an object of the present invention to provide animproved form of fish pass.

SUMMARY OF THE INVENTION

According to the present invention there is provided a fish pass whichcomprises material that augments a significant part of the crest of awater penning control structure and a channel component to convey waterdownstream of the water penning control structure, the channel componenthaving a hinged attachment to the crest of the water penning controlstructure.

A buoyancy unit is preferably attached adjustably to the channelcomponent.

The channel component is preferably lined with a bristle substrate, andthe bristle substrate is preferably not parallel to the base of thechannel component.

The fish pass may also include an upstream element that is movablepivotally relative to the channel component, and a gearbox unit may beprovided for effecting controlled movement of the upstream elementrelative to the channel component.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of an eel pass in accordance with a firstembodiment of the present invention,

FIG. 2 is a side elevation of the eel pass of FIG. 1 mounted on atilting weir gate showing how the eel pass functions at two differentwater penning heights,

FIG. 3 is a sectional view of the main channel of the eel pass of FIG.1, showing different substrate arrangements and different channelwidths,

FIG. 4 is a sectional view of part of a tilting weir gate, showingtypical attachment options for the weir crest augmentation material,

FIG. 5 is a perspective view of an eel pass in accordance with a secondembodiment of the present invention,

FIG. 6 is a perspective view of a gearbox that forms part of the eelpass of FIG. 5,

FIG. 7 is a perspective view of the gearbox of FIG. 6, but with thehousing cover removed, and

FIG. 8 is a reverse perspective view of the gearbox of FIG. 6, with thehousing cover and the shaft-end housing removed.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The eel pass shown in FIGS. 1 to 4 of the drawings comprises two strips1 of weir crest augmentation material that are attached by suitablefixings 8, 13 to the crest of a tilting weir 11 or other appropriatewater level control structure. A main channel 3 is hingedly connected at2 to the weir crest augmentation material, with the hinge being atsubstantially the same level as the top of the tilting weir 11. Thechannel 3 is thus arranged for pivotal movement relative to thenon-augmented section of the weir crest. The inside of the main channel3 is lined with an appropriate bristle substrate 7 and the ends of themain channel 3 are partially blanked off by means of triangular endstops 6. The bristle substrate 7 carries two densities of bristles tocater for different sizes of eels and the bristle substrate 7 is fixedin a sloping arrangement to allow for different water flow rates downthe channel 3. The bristles are thus inclined to the vertical so that,in cross-section, the upper surfaces of the bristles are either ofV-shaped formation, or inverted V-shape, as shown in FIG. 3.

The two strips 1 of weir crest augmentation material, which may be ofwood or a suitable plastics material, effectively serve to raise theheight of the weir for substantially the whole width of the weir so thatthe majority of the water flowing over the weir passes down the channel3.

There is a planar lid or cover component 7A that is hingedly orotherwise attached to the main body of the channel 3 and this protectsthe ascending eels from desiccation and predation. The lid or covercomponent 7A is removable to facilitate cleaning of the eel pass.

Adjacent the downstream end of the channel 3 of the eel pass, there isan adjustable buoyancy unit 4 in the form of a hollow cylinder that isattached by means of an adjustment carriage 5 to guide slots in thesides of the main channel 3. The flotation effect of the buoyancy unit 4can be adjusted for varying conditions by moving the carriage 5 alongthe guide slots.

The eel pass includes an upstream element 10 that is hingedly connectedat 9 to the weir crest augmentation material, with the hinge being atsubstantially the same level as the top of the tilting weir 11. Theupstream element 10 also has a covering of bristle substrate and thefunction of the upstream element 10 is to ensure that eels which havepassed up the main channel 3 can get far enough away from the weir flowthat they do not get swept back downstream. The upstream element 10 maybe fixed at a pre-set angle or may be adjustable by altering its weightor profile.

The tilting weir 11 is arranged to pivot about a pivot axis 12 and FIG.2 shows how, with the tilting weir 11 arcing around the pivot point 12,the eel pass will still maintain a water flow down the channel 3 whichwill remain at a suitable gradient. The line indicated at W3 in FIG. 2represents the downstream water level while the lines W1 and W2represent two different penned water levels.

FIG. 4 illustrates two possible methods of attaching the weir crestaugmentation material 1 and the hinges 2 and 9 to the top surface of theweir 11 or other water penning control structure. Fixing screws 8 can bedriven through the weir crest augmentation material 1 into the body ofthe water penning control structure 11, or an appropriately dimensionedH-section extrusion 13 can be attached to the structure 11, with theweir crest augmentation material 1 attached to the H-section extrusion13.

An important advantage of the eel pass described above and shown inFIGS. 1 to 4 is that it can easily be retro-fitted to existingstructures in situ rather than replacing the entire tilting weir 11 orother water level control structure. The eel pass can also be factoryfitted for a new installation.

Although specific reference has been made to the use of the device ofthe present invention to assist upstream movement of eels, the pass canbe used to assist upstream movement of fish generally.

The eel pass (or fish pass) shown in FIGS. 5 to 8 differs from thatshown in FIGS. 1 to 4 in that it includes a gearbox unit for effectingrelative movements of the components of the eel pass. The purpose of thegearbox unit is to transmit the effects of a change in weir angle,registered by the downstream end of the eel pass, to the upstreamcomponent, thereby ensuring that this component is always angleddownwards into the upstream water body.

This will allow eels or other fish to ascend the pass to its apex andenable them to crawl or swim beyond the influence of the weir crestflow.

The whole gearbox unit can be raised or lowered according to water flowconditions and the position or influence of the weir crest augmentationmaterial.

As shown in FIGS. 6 to 8, the gearbox unit that comprises gears G1,seated in a gear housing G2 to which a gear housing cover G2 a isattached. The gearbox unit includes a downstream shaft G3, which is theattachment point for the downstream element of the eel pass. This shaftG3 transmits movement from a tilting weir in relation to the downstreamelement 3 of the eel fish pass to the appropriate gear. Because thegears G1 are interlinked this movement is transferred to an upstreamshaft G4. The upstream element 10 of the eel pass is attached to thisshaft G4 and deflects accordingly. The size and number of gears G1 canbe calculated to provide an approximately constant downwards angle inthe upstream element of the eel pass, regardless of the tilting angle ofthe weir.

Both shafts G3 and G4 are supported on the non-geared side by ashaft-end housing G5. The gears G1 in their housing G2, the shafts G3and G4 and the shaft-end housing G5 can all be raised and lowered inrelation to a weir fixing bracket G6 by the rotation of adjuster screwsG7 and G8. Rotation of the screws G7 and G8 will allow either more orless water to flow down the eel pass. The adjuster screws G7 and G8 passthrough captive threaded blocks G9 and G10 which are recessed intohousings G2 and G5. The adjuster screws G7 and G8 terminate in the weirbracket G6 and the raising and lowering action is stabilized andsupported by four guide pins G11, G12, G13 and G14. These guide pins arefixed into the weir bracket G6.

FIG. 5 shows the gearbox unit of FIGS. 6 to 8 attached to and actingbetween a downstream main channel component 3, to which a buoyancy unit4 is adjustably attached, and an upstream channel component 10, withbristle assemblies contained within both channel components 3 and 10.

1. A fish pass which comprises material that augments a significant partof the crest of a water penning control structure and a channelcomponent to convey water downstream of the water penning controlstructure, the channel component having a hinged attachment to the crestof the water penning control structure.
 2. A fish pass as claimed inclaim 1, in which a buoyancy unit is attached to the channel component.3. A fish pass as claimed in claim 2, in which the buoyancy unit isattached adjustably to the channel component.
 4. A fish pass as claimedin claim 1, in which the channel component is lined with a bristlesubstrate.
 5. A fish pass as claimed in claim 4, in which the bristlesubstrate is not parallel to the base of the channel component.
 6. Afish pass as claimed in claim 5, which includes triangular end stopsthat partially blank off the upstream end of the channel component.
 7. Afish pass as claimed in claim 1, which includes an upstream element thatis movable pivotally relative to the channel component.
 8. A fish passas claimed in claim 7, which includes a gearbox unit for effectingcontrolled movement of the upstream element relative to the channelcomponent.
 9. A fish pass as claimed in claim 7, in which the upstreamelement is of channel formation and contains a bristle substrate.
 10. Afish pass as claimed in claim 1, which includes a cover removably fittedto the channel component.